1. Field of the Invention
The present invention relates to a zoom lens system, having a short back focal length, of a compact camera; and in particular, a low cost zoom lens system having a zoom ratio ranging from about 2.5 to 3.
2. Description of the Related Art
A zoom lens system of a compact camera differs from that of a single-reflex camera in that the lens arrangement of a compact camera has more freedom of design due to fewer constraints on a back focal length (a short back focal length is acceptable). In a zoom lens system having a positive first lens group and a negative second lens group (two-lens-group type) in order from the object side, there are advantages, such as fewer lens elements, being small and compact, and the manufacture thereof being simple. For a zoom lens system, in the prior art, having a half-angle-of-view of about 30.degree. at the short focal-length extremity (wide-angle extremity) and a zoom ratio ranging from about 2.5 to 3, a three-lens-group type has usually been employed in order to improve the optical performance thereof. In the three-lens-group type zoom lens system, the traveling distance of the third lens group can be reduced, so that the F-number at the long focal-length extremity (telephoto extremity) can be made smaller (brighter) , and the fluctuations of aberrations upon zooming between the wide extremity and the telephoto extremity can be reduced. However, when comparing the three-lens-group type with the two-lens-group type, the former is larger in size and more complicated in the lens arrangement than the latter, which means that the number of lens elements has to be increased, and the size of the front most lens group (the first lens group) is increased. All of these factors have resulted in an increase of the overall manufacturing costs.